Today, several main types of sensors or pickups are used for electric stringed musical instruments which allow to receive and process an electric signal corresponding to a string vibration, such as electromagnetic, piezoelectric and optical sensors.
Said types of sensors are well-suited for traditional electric guitars and allow to reproduce acoustic sounds of a string quite naturally.
However, when it comes to MIDI instruments, the solutions known in the art have a number of significant drawbacks or limitations.
As one of essential requirements for MIDI instruments according to the signal processing algorithm, it is important to form a separate signal from each individual string. In this case, there should be no, or at least minimized, mutual influences of vibrations of other strings on a signal produced by a particular string, regardless of the nature of such influences. The influence of the sensor itself on string vibrations is also undesirable.
Standard electromagnetic and piezoelectric sensors cannot provide a high-quality separation of signals produced by individual strings due to the presence of electromagnetic or mechanical effects of vibrations of one string on the formation of signals by other strings. When polyphonic sensors having a separate sensor (an electromagnetic coil or a piezoelectric sensor) are used for each string, the influence of one string on the signal formation by other strings is reduced substantially; however complete interference is still not achieved.
Further, to minimize delays in sound generation based on processed string vibration signal, the sensor should provide, as far as possible, dynamic information on a change of a signal (vibrations) as well as static data on deflections of a string from its initial (“zero”) position at different points of time. This data allows to determine the mechanical parameters of the system before and at the moment of influence on a string (“pinch”, “hit”, touch to a string) more accurately and, respectively, to form the basic characteristics of the corresponding generated acoustic signal with a lower delay and as accurately as possible: height, volume, level of attack, and duration of sound.
Further, for MIDI instruments, in terms of a comprehensive analysis of the mechanical influence exerted on a string by a musician, it is useful to have information in at least two planes—horizontal and vertical. This allows to distinguish between different types of influence (“pinch”, “hit”, touch to a string) and, accordingly, to adjust parameters of the acoustic signal so generated. This information is also very useful to analyze the influence on a string on a neck of a stringed instrument (shifting a string, pressing a string), which, along with the signals from other sensors of a MIDI controller, allows to more fully use playing techniques used when playing on a standard acoustic or electric guitar (bending, tremolo, “hammer-on”, “pull off” and others). Electromagnetic and piezoelectric sensors, in their standard embodiments, cannot provide said data given physical constraints and principles of operation.
Optical sensors (a signal pickup is achieved using the effect of a light beam reflected from a vibrating string on a light-sensitive element) can provide a high-quality separation of a signal produced by individual strings and avoid the influence of a sensor on a string. However, such sensors, known in the art, are of fairly large size and require the placement of optical emitters and receivers directly above, under, or along the sides of a string. Such placement makes an instrument bulky and inconvenient to use.
The prior art discloses a large number of technical solutions related to optical sensors and stringed musical instruments equipped with said sensors, including: FR2845194A1 dd. Apr. 2, 2004; UA23109 dd. May 10, 2007; U.S. Pat. No. 4,630,520 dd. Dec. 23, 1986; U.S. Pat. No. 4,730,530 dd. Mar. 15, 1988; U.S. Pat. No. 5,237,126 dd. Aug. 17, 1993; U.S. Pat. No. 7,129,468 dd. Dec. 31, 2006; U.S. Pat. No. 8,071,870 dd. Dec. 6, 2011; US2012266740 dd. Oct. 25, 2012; US2015317967 dd. Nov. 5, 2015 and others.
The prior art discloses an optical pickup for a stringed instrument for producing information as to the frequency of vibration of a string thereof, comprising: optical emitter means for producing a light beam of 1-5 mm aperture, located so that said string passes in and out of said light beam when said string is vibrating; and optical detector means for detecting said optical field produced by said optical emitter means after being modulated by the motion of said string and converting said detecting optical field into an signal, said emitter means and detector means being arranged such that the plane of said optical emitter means and said optical detector means is substantially parallel to the plane of the strings of said instrument (U.S. Pat. No. 4,688,460 dd. Aug. 25, 1987).
A technical solution disclosed in U.S. Pat. No. 5,214,232 dd. May 25, 1993, was taken as a prototype, specifically: an electric stringed musical instrument comprising a body, at least one string stretched over said body, a detecting unit fixed to said body, and located below said at least one string, said detecting unit having at least one photo emitting element for radiating light toward said at least one string, and a photo detecting element for receiving reflection of said light from said at least one string and producing photo current indicative of the intensity of said reflection, said intensity of said reflection being varied when said at least one string is vibrated, variation of said reflection being indicative of vibrations of said at least one string in both lateral and vertical directions, and sound producing means supplied with said photo current for producing sounds, said photo detecting element having a detectable range for a minimum intensity of said reflection, said at least one string being located at a midpoint evenly spaced apart from a boundary of said detectable range in directions on a virtual plane substantially parallel thereto when remaining stationary, and said photo detecting element having a focal point beyond said at least one string, said photo current being increased along plots having a linear zone toward said focal point with said at least one string being vibrated within said linear zone.
The disadvantages of said prior art and the prototype are the inability to obtain distinct separate signals that would correspond to deflections (vibrations) of a string in two mutually perpendicular planes. A signal formed as current generated by illumination of the light-receiving element by reflected radiation does not allow to clearly distinguish vibrations in two mutually perpendicular planes and, accordingly, to form such acoustic vibrations with sound-producing means that would correspond to actual vibrations of a string in space.